Cathodic electrocoating composition compounded with latex binder and possessing enhanced gloss

ABSTRACT

An improved cathodic electrocoating composition comprises an aqueous suspension of synthetic, cation-active, film-forming latex particles characterized by a latex gel content that is not substantially above about 10%.

This invention relates to an improvement in aqueous cathodicelectrocoating composition, more particularly to same containing asuspension of film-forming synthetic latex particles, and electrocoatingwith said composition.

BACKGROUND OF THE INVENTION

The application of protective and decorative coatings in the nature ofpaint or varnish by electrophoretic deposition now is a large industry.Quite commonly such coating processes are called "electrocoating". U.S.Patent and Trandmark Office Class 204, subclass 181, relfects the largegrowth of this technology in recent years.

Generally, in an electrocoating process of the type concerned here, oneor more cathode workpieces and one or more counterelectrodes (anodes)are maintained for a short period of time in an electrical circuit witha dilute aqueous dispersion of film-forming paint binder, usuallypigmented, between them. In most such coating operations a netunidirectional electric current is passed between these electrodes atfair voltage (e.g., 50+V.). Generally such current is rectified accurrent. This causes deposition of the coating on the electrodes(workpieces). Most frequently the binder dispersion is maintained as abath in which the electrodes are at least partially immersed. Othermethods for forming the electrical circuit also have been proposed,e.g., by showering the workpieces with continuous streams of thecurrent-carrying aqueous coating dispersion.

Representative of the earliest practical electrocoating is that shown inAllan E. Gilchrist's U.S. Pat. No. 3,230,162 of 1966. More recentlycationic or cathodic electrocoating has become popular. U.S. Pat. No.3,799,854 and many subsequent patents involving the electrodeposition ofblocked isocyanate and amino resins onto a cathodic workpiece, and thesubsequent curing of the electrodeposited film into a crosslinkedstructure are representative of such cathodic electrocoating. These verypractical techniques employ comparatively low molecular weight,structurally ionized resinous material as their fundamental paintbinders for the electrocoating, in contrast to the instant latices madeby emulsion polymerization.

That is not to say that the cathodic electrodeposition of syntheticlatices has not been proposed before. Representative cathodicelectrocoating proposals using synthetic latex binders include those ofthese U.S. patents: Nos. 3,873,488; 3,882,009; 3,994,792; 3,998,776;4,017,372; 4,225,406; and 4,225,407.

Synthetic latics made by emulsion polymerization as cathodicelectrocoating binders have been regarded as having the inherentpotential of possessing a number of desirable characteristics such ashigh coulombic efficiency, high molecular weight for various properties,crosslinkability if desired, low cost, and versatility of composition.

In the emulsion polymerization of cathodic electrocoating laticesappreciable amounts of gels (microgels) often form. This intractablematerial has very high molecular weight. We have found that formost lowgloss applications such gel can be tolerated, but it seriously detractsfrom the ability to obtain optimum gloss and smoothness, as for aone-coat finish. The presence of gel can be assessed conveniently bycasting the film of the latex on an aluminum sheet, extracting withacetone, and noting the weight of undissolved residual polymer.

Advantages of the instant invention over prior synthetic cathodicelectrocoating latex compositions include the capacity to produceoptimally glossy films in a highly efficient manner; additionally, theelectrodeposited films of the inventive compositions appear to haveenhanced solvent resistance.

BROAD STATEMENT OF THE INVENTION

The instant invention is a cathodic electrocoating compositioncomprising an aqueous suspension of synthetic cation-active,film-forming latex particles characterized by latex gel content that isnot substantially above about 10%, and preferably is mush less.

DETAILED DESCRIPTION OF THE INVENTION

The instant latex is prepared by emulsion polymerization of additionpolymerizable materials in aqueous dispersion, preferably ethylenicallyunsaturated monomers. The latex should be film-forming on a cathodeduring the wet electrocoating operation, that is it should have a Tg ofabout -40° to +60° C. and preferably about -10° to +30° C. The latex iscation-active by virtue of being amino-stabilized. By this is meant thatsuch cation activity is provided fundamentally by a small proportion ofamino, amidino, and/or guanadino functionality that is structurally apart of the latex molecule and/or is sorbed onto the surface of thelatex, as in the form of a surfactant having such functionality.Additional cation activity also can be imparted by, for example, betahydroxyethyl quaternary ammonium functionality of the latex and/or suchsorbed surfactant.

Representative nonionic monomer types useful for forming suitablelatices include alkenyl aromatic compounds such as styrene compounds;derivatives of alpha-methylene monocarboxylic acids such as acrylicesters, acrylic nitriles, and methacrylic esters; derivatives of alpha-,beta-ethylenically unsaturated dicarboxylic acids such as maleic estersand unsaturated alcohol esters; conjugated dienes; unsaturated ketones;unsaturated ethers; and other polymerizable vinylidene compounds such asvinyl chloride and vinyl fluoride. Specific ethylenically unsaturatedcompounds useful for the instant latices include styrene,alpha-methylstyrene, para-methylstyrene, ethylstyrene, diethylstyrene,t-butylstyrene, vinylnaphthalene, hydroxystyrene, methoxystyrene,cyanostyrene, acetylstyrene, monochlorostyrene, dichlorostyrene, andother halostyrenes, methyl methacrylate, ethyl acrylate, butyl acrylate,hexyl acrylate, 2-ethylhexyl acrylate, lauryl methacrylate, phenylacrylate, 2-hydroxybutyl acrylate, 2-hydroxybutyl methacrylate,4-hydroxybutyl acrylate, and 4-hydroxybutyl methacrylate; acrylonitrile,methacrylonitrile, acryloanilide, ethyl alpha-chlorocrylate, ethylmaleate, vinyl acetate, vinyl propionate, vinyl chloride, vinyl bromide,vinylidene chloride, vinylidene fluoride, vinyl methyl ketone, methylisopropenyl ketone, vinyl ethyl ether, 1,3-butadiene, and isoprene.Styrene units are especially desirable in copolymers for the instantservice, not only because styrene is economical, but also because ithelps to impart gloss to the cured coating.

Most of the foregoing nonionic monomers tend to form water-insolublepolymers, and they are usually copolymerized with monomers havinghydrophilic character for the purpose of, amongst other things,crosslinking capability and/or providing the needed cation activity.Representative of such modifying monomers are hydroxyethyl acrylate,hydroxyethyl methacrylate, hydroxypropyl methacrylate, acrylamide,methacrylamide, and modified acrylamides such as diacetone acrylamideand diacetone methacrylamide, and dimethylaminoethyl methacrylate,diethylaminoethyl methacrylate, t-butylaminoethyl methacrylate,isopropylaminopropyl methacrylamide, dimethylaminopropyl methacrylamide.

Hydrophilic monomer units in the latex structure that are notcharge-bearing, e.g., those having hydroxyl and/or acrylamidefunctionality, can be used in modest levels; typically they are broadlyused to constitute between about 2 and about 30 weight percent of theresulting thermosetting latex polymer solids and advantageously about5-15%. The charge-bearing hydrophilic monomers for making a latexstructurally cation-active desirably are used in a proportion of no morethan about 5% by weight of the latex polymer solids, and preferably theyamount to 0.5% or even less. Thus the resulting latex, in spite of thesemodifications, can be considered hydrophobic.

Emulsion polymerization to make the latex generally is carried on in areaction zone with agitation at atmospheric pressure using a temperatureof about 25° to 90° C. Typically the monomers are charged gradually toan aqueous body which can contain all of the water or only an initialfraction of it, such fraction being augmented as the reaction continues.Initiator for the latex polymerization can be present initially in theaqueous body, and it also can be added concurrently with the monomercharge. So can surfactant if surfactant is to be used at all. Apreferred latex preparation is a seeded semi-continuous emulsionpolymerization wherein about 0.5-10% of the monomer is used to establisha polymerized seed population by emulsion polymerization, then the restof the ingredients are added to the recipe to form polymer upon theseeds. Small amounts of surfactants such as fatty imidazolines,ethoxylated fatty guanadines (e.g. Aerosol C61, a trademark of AmericalCyanamid Company), nonionics such as highly ethoxylated octyl and nonylphenols, ethoxylated fatty alcohols, and amine-functional polymericsurfactants also can be used if necessary or desirable. In the instantlatices the concentration of oligomeric or polymeric starting materialis quite low (not substantially above about 5%, e.g., from oligomeric orpolymeric surfactant), the vast preponderance of the latex provided bythe monomers charged.

Conventional additives for latex compositions can be included in theemulsion polymerization recipe, and some can be added later. Suchmaterials include chain transfer agents, shortstopping agents, buffers,antifoaming agents, chelating agents, plasticizers, tinting materials,and bactericides or other preservatives. In a preferred operation a heelof partially-reacted latex is used (thereby providing a preformed seed);additional water, the rest of the monomers and often additionalsurfactants and initiators then are the customary feeds in incrementalor continuous fashion while the contents of the polymerization zone areagitated under conditions of temperature and pressure suitable formaintaining the polymerization. Preferably the temperature for theparticular initiator system and polymerization is between about 70andabout 85° C. and the pressure is atmospheric, although higherpressures, and thus temperatures are possible. Advantageously the rateof monomer addition is low enough to control the rate of polymerization.

Chain transfer agents conventionally have been used to control molecularweight of latics, thus tending to suppress gel formation. However, webelieve that the adverse effect of even very minor proportions of gel inlatics for cathodic electrocoating has never been reported heretofore,assuming it was even noted previously. It is not surprising that sucheffect might go unnoticed; the same latices with modest gel contents,applied by brush or cast by drawdown bar in air, give no specialproblems or bad effects. Apparently the deposition and coalescenceaction of such latices under water, (as in an electrocoating bath)differ substantially from the corresponding action in air and are farmore sensitive to the presence of a little gel.

The initiators produce free radicals for the latex polymerization andcan be, for example, certain redox systems such as: hydroxylaminehydrochloride in combination with t-butylhydroperoxide, azo types suchas 2,2'-azobis (amidinopropane hydrochloride) ("AAP"), 2,2'-azobisisobutyronitrile ("AIBN"), 2,2'-azobis (2-isopropylimidazolium)dichloride, 2,2'-azobic (2-aminopropane) sulfate, or even an electronbeam or gamma radiation. The latex is prepared at a polymer solids (NV)content that usually is at least about 35%, preferably about 40-60%, andeven as high as about 70% in some cases. pH of a finished latex batchfor the electrocoating purpose usually will be between about 1 and about6, and generally will be between about 2 and about 5. For theelectrodeposition process latex emulsions are diluted with water to asolids concentration generally not above about 25% and advantageouslybetween 1 and 15%.

latex particle size advantageously averages (weight average) betweenabout 1000 Å and about 4000 Å although ones from 300 Å to 6000 Åuseable. By use of appropirate monomeric material in their preparationsfunctionality can be incorporated into the molecular structures of thelatex and the resinous pigment dispersant for rendering these structurescrosslinkable with each other or self-crosslinking. Thus, for example,blocked isocyanate functionality so incorporated can be made tocrosslink upon curing with labile hydrogen functionality such ashydroxyl, unhindered secondary amine, amide, and/or thiol funtionalitypresent. If both sorts of functionality are part of the same molecularstructure, that structure will be self-crosslinkable; if one sort suchas the blocked isocyanate is part of one structure and the other such aslabile hydrogen is part of another polymer molecule, these diversestructures can be crosslinked with each other. Typical blockedisocyanate monomers for such use are, for example, 2-isocyanatoethylmethacrylate blocked with 2-butanone ketoxime or the adduct of eithertoluene diisocyanate or isophorone diisocyanate havine one isocyanategroup reacted with hydroxyethyl methacrylate and the other blocked withcaprolactam or other blocking compound such as an oxime. Amethylolacrylamide such as isobutoxyl methylolacrylamide also can beused, but as such funtionality generally crosslinks most satisfactorilywith some acidity present and often tends to give appreciable microgelformation, blocked isocyanates are preferred. Hydroxy functionalacrylates are the preferred labile hydrogen-providing materials for apolymerization.

Curiously, however, it has been found that only a limited proportion ofresinous pigment dispersant can be electrodeposited with latex foreffective crosslinking therewith before solvent resistance of the curedfilm will be markedly adversely affected. Thus, when a dispersantproportion amounts to no more than about 150% of the latex crosslinkabletherewith, the solvent resistance of the cured film is lowered somewhat,but such loss usually can be tolerated. However, when an appreciablygreater proportion of such dispersant is present, the solvent resistanceof the cured film is very badly affected-unless the electrodeposit alsocontains some additional material, i.e., an external crosslinker, thatwill crosslink with at least the dispersant upon curing. Useful externalcrosslinkers include acid functional aminoplasts, e.g., melamine resinssuch as Cymel 1141, a tradmark of American Cyanamid Company, or ablocked isocyanate such as isophorone diisocyanate blocked with epsiloncaprolactam or other conventional blocking agent.

Solvent resistance of the cured film also can be obtained by use of suchexternal crosslinker that has been codeposited with latex and resinouspigment dispersant that will not crosslink with each other, but willcrosslink with such external crosslinker film component.

As noted above, adequate cation activity for the latex can be providedby a very small porportion of amino, amidino, and/or guanadinofunctionality that is structurally a part of the latex molecule and/orsorbed onto the surface of the latex. Polymerizing charge-bearinghydrophilic monomer units into the latex structure certainly is thepositive way for imparting the needed cation activity thereto. It shouldbe noted, also, that initiators such as 2,2'-azobis (amidinopropanehydrochloride) (AAP) break down in use to provide structural amidinofunctionality in the polymer while the fatty imidazoline surfactants cansupply useful amidino functionality for sorption onto the surface oflatex having otherwise little or no cation activity. Similarly,ethoxylated fatty guanadine surfactants can impart guanadinofunctionality to the surface of such latices for rendering or helping torender them adequately cation active.

Suitable resinous pigment dispersants (pigment grind vehicles) for theinstant invention will have functionality that is crosslinkable withthat of a latex or an external crosslinker. Advantageous resins for suchservice include acrylic resins having some hydroxyl functionality andaverage mol weight of about 2000 to 5000, and epoxy resins modified withan amine, such epoxy resin having average mol weight of about 800-1600.An electrocoating binder of the present invention ordinarily will bepredominantly latex with the corsslinkable dispersant being from about0.1 to 40% and preferably about 5 to 30% of the binder and the externalcrosslinker if needed, being about 5 to 30% and preferably about 5 to25% of the binder.

Customarily the wet electrocoated part is drained, blown with air toremove loosely adhering liquid, and/or rinsed. Advantageously the finalrinse is with deionized water. Rinsing also can be done with a permeatefrom ultrafiltration of an electrocoat bath. Initial rinsing can be donewith an aqueous dispersion recovered from later rinsing, e.g., from thefinal rinse.

Cure of the wet electrodeposit to its final dry and hardened stategenerally is done by baking the coated article at about 120° to 230° C.for 5 to 40 minutes, although radiation curing also is possible, e.g.,by electron beam, gamma radiation, or by ultriviolet light if asensitizer is incorporated into the film and the light is not masked bypigmentation.

Pigmentation for the electrocoating composition typically can beprovided by mixing therein pigments such as titanium dioxide, ironoxides, lead chromate, carbon black, cadmium yellows and reds, clay,silica, talc, phthalocyanine blue, chromium yellow, aluminum flake, andother conventional pigmentary materials and even fine particles of hardpolymer or resin, some of which can be caused to fuse upon curing oreven to crosslink with other electrodeposited materials if desired.While such pigmentary materials usually form a minor proportion of thepaint solids that are to be electrocoated, they can on occasionconstitute a major proportion, especially where a plastic pigment fusesand/or reacts upon curing to give additional binding to the particlespresent. Pigments, particularly mineral pigments, usually are added tothe electrocoating composition in the form of a pigment grind using aresinous vehicle that has molecular weight substantially below that ofthe latex.

Counterions for amino functionality in the coating composition areprovided in the composition by acids such as formic, acetic, lactic,and/or phosphoric acids. pH of a typical composition of this inventionfor the instant pigmented cathodic electrocoating will be between about3 and about 6, and generally it is advantageous to be about 4 to 5, withabout 1 meq. of acid per meq. of base present.

The presence of solvents such as alkoxyalkanols, hydrocarbons such as amaphtha or toluene, or an acetate such as butyl acetate tends to lowerthe rupture voltage of the electrodeposited latex film. Hence, little orno solvent is preferred in manufacture of the latex, and any solventconcentration in the electrocoating composition, based on weight ofnonvolatile matter, best is limited to about 15% by weight, maximum.Such solvent customarily is introduced into a formula with a pigmentgrind.

Desirably the free monomer in the latex, and, thus, in the cathodicelectrocoating composition, is maintained very low. By using one or moreclean-up procedures at the end of the latex polymerization, one canaccomplish this. One such procedure is to treat the latex finally with aseries of successive small initiator additions and to raise the finaltemperature for reacting virtually all of the free monomer present, ifnot all. Other useful techniques include adding a small proportion ofhighly reactive monomers such as an acrylate to combine with, forexample, free vinyl acetate, or to stop a styrene feed near the end ofthe latex-making reaction (because such monomer can inhibit the completepolymerization of other less reactive monomers present). Vacuumstripping is an alternate method of free monomer removal. Gaschromatography is useful for determining the level of residual monomer,Gas chromatography is useful for determining the level of residualmonomer, which desirably is not more than about 2% and is preferred tobe much less.

For the highest quality of cathodic electrodeposition desired here it isespecially important to remove amino monomers and amino initiatorfragments, which can impart roughness to a cathodically-electrodepositedfilm of the latex; "amino" is used here in the broad sense to comprehendmonomers and fragments of molecular weight not above 300 and havingamino, guanadino, and/or amidino functionality, and, in general,nitrogenous functionality that is basically-reaction in aqueousdispersion. When such monomer is fully reacted, it is effectivelysequestered. Ion exchange of the latex with an ion exchange resin inacid form is useful for eliminating virtually all of the free aminomonomer and amino initiator fragments; these should not be substantiallyabove about 0.1% of the latex solids.

As mentioned above, an electrocoating bath composition hereadvantgeously will contain about 1 to 15% by weight of solids. Thereplenishment feed composition for an instant cathodic electrocoatingbath will have greater concentration than this, and it can reach 50-60%of such solids. By using a replenishment composition deficient in acidrelative to ionizable amino, guanadino, and/or amidino group in suchreplenishment composition, one can help to keep the buildup of acid inan operating bath under control. The bath also can be purged by use ofmembranes which will permit bath components to be withdrawn quiteselectively as by ultrafiltration.

The following examples illustrate the invention, but should not beconstrued as limiting it. In this specification all percentages areweight percentages, all parts are parts by weight, and all temperaturesare in degrees C. unless otherwise expressly indicated. In the examplesthe electrocoating test tank held a liter of paint dispersion. The tankwas divided into a larger dipping section and a smaller agitator sectionby a vertical wier to one side that fixed the depth of the paintingbath. The wier was short of the bottom of the tank to permitrecirculation of bath dispersion from the agitator section into thebottom of the dipping section. Paint dispersion flowed over the wierinto the agitator section, then was impelled downwardly by apropellor-type agitator into the bottom of the dipping secton. Thiscreated a circulation of the paint dispersion with a level top surfacein the dipping section.

A 4"×4" (10.2 cm) conventionally phosphated (Parker Bonderite 1000 ironphosphated) 20 ga. (0.95 mm.) steel panel was lowered over about 9seconds to a depth of 31/2" (8.9 cm.) with power on, the immersion beingmade about centrally to the wall confines of the dipping section of thetank. The tank was charged as an anode and panel as a cathode withconstant voltage impressed therebetween. Power was left on for 64seconds after a panel was fully immersed, then turned off and the wetcoated panel withdrawn from the bath. It was rinsed with deionizedwater. Each panel was baked for 20 minutes at a temperature between 150°and 190° to cure the resulting wet electrodeposited film.

The electrocoating process was very rapid. The wet coating wassubstantially complete in a few seconds after a panel had been immersedto the final depth (with attendant virtually complete shutoff of currentin the circuit). The cured coatings were ostensibly perfect and smooth.Their thicknesses were from approximately 1/2 mil (0.013 mm.) to 11/2mils (0.038 mm.), depending upon the particular test conditions.

Each latex was diluted with deionized water to make a coatingcomposition having 5% solids (NV) content. For each coating compositiontested panels were electrocoated from a 25° C. bath at the followingconstant voltages: 100, 150, 200, and 250; and from a 45° C. bath atvoltages of 200 and 300. The 60° gloss of a cured coating was measuredwith a Hunter laboratory D48D gloss meter standardized with a blackglass plate. Glosses were averaged for a particular coating composition.That average is the number for gloss value reported in the exampleswhich follow. The gloss test used was the ASTM-523-80 60° specular glosstest.

Gel content of a latex was measured by casting a film of the latex witha No. 38 wire-wound drawdown bar onto aluminum foil, air drying the filmfor 2 hours, immersing the thus-coating coil in acetone at roomtemerature for three days, then ascertaining the undissolved polymerremaining as a percentage of the dried latex. Two determinations weremade for each latex except in Example 5 where only one was made.

EXAMPLES 1-12

Twelve latices were prepared according to the recipes tabulated below.In these prepartions the Group A ingredients for each latex were heatedin an agitated reactor to 75° C. which was sparged with nitrogen.Thereafter a nitrogen gas blanket was maintained over the agitatedreaction mixture. The Group B ingredients were added, and, after about 5minutes, the Group C ingredients. This was followed by a 4-hour additionof the group D ingredients and, starting simultaneously with the Group Dingredients, a 41/2-hour addition of the Group E ingredients. After theaddition of the Group E ingredients had been completed, the mixture washeld at 75° with agitaton for about 1 hour then cooled to roomtemperature. The synthetic latices of the resulting emulsions each hadweight average molecular weight estimated to be well above 100,000. Thelatex solids content of a dispersion, like the other nonvolatile mattercontents ("NV") referred to in this specification, can be determinedfrom the weight remaining after evaporating volatile matter at 125° C.for 30 minutes from a thin film of sample inhibited against furtherpolymerization with hydroquinone. The phosphoric acid in the laticesamounted to one meq. of its first hydrogen per meq. of base present.

                  TABLE I                                                         ______________________________________                                                                Parts per 100 parts                                   Group Ingredients       of Monomer                                            ______________________________________                                        A     Deionized Water         134.0                                                 Triton X-405*           0.1                                                   H.sub.3 PO.sub.4 (85.6% solution                                                                      0.1                                                   in water)                                                               B     Butyl Acrylate (BA)     0.7                                                   Methyl Methacrylate     1.3                                                   (MMA)                                                                         CBr.sub.4 (for Example 1 only)                                                                        1.0                                             C     Deionized Water         4.2                                                   AAP.sup.a               0.1                                             D     As tabulated in Table II for                                                  each Example                                                            E     Deionized Water         11.4                                                  Triton X-405*           1.3                                                   AAP.sup.a               0.3   for Examples                                                                  1-4, inclusive                                                          0.2   for Examples                                                                  5-9, inclusive                            ______________________________________                                         .sup.a 2,2'-azobis (2amidino propane hydrochloride)                           *The trademark of Rohm & Haas Company for the nonionic surfactant,            ethoxylated octylphenol having an average of 40 mols of ethylene oxide pe     mol of the phenol.                                                       

                                      TABLE II                                    __________________________________________________________________________    Group D Ingredients for each Example                                          Example    Parts per 100 parts of Monomer                                     Ingredients                                                                         No.  1  2  3   4  5  6  7  8  9  10 11 12                               __________________________________________________________________________    BA         49.2                                                                             49.2                                                                             49.2                                                                              49.2                                                                             48.9                                                                             48.5                                                                             44.7                                                                             47.0                                                                             46.3                                                                             49.5                                                                             48.1                                                                             49.8                             MMA        32.7                                                                             32.7                                                                             32.7                                                                              32.7                                                                             31.5                                                                             28.6                                                                             34.4                                                                             38.3                                                                             35.3                                                                             34.5                                                                             38.9                                                                             36.4                             HPMA.sup.a 8.6                                                                              8.6                                                                              8.6 8.6                                                                               6.5                                                                              9.8                                                                             -- -- -- 6.5                                                                              -- 4.3                              HEA.sup.b  -- -- --  -- -- --  7.9                                                                             5.2                                                                               5.2                                                                             -- 3.5                                                                              --                               BIEM.sup.c 7.3                                                                              7.3                                                                              7.3 7.3                                                                              10.9                                                                             10.9                                                                             10.9                                                                             7.3                                                                              10.9                                                                             7.3                                                                              7.3                                                                              7.3                              DMAEMA.sup.d                                                                             0.2                                                                              0.2                                                                              0.2 0.2                                                                               0.2                                                                              0.2                                                                              0.2                                                                             0.2                                                                               0.2                                                                             0.2                                                                              0.2                                                                              0.2                              n-Dodecyl Mercaptan                                                                      0.2                                                                              0.2                                                                              0.6 0.2                                                                              --  0.7                                                                             -- 0.7                                                                               0.7                                                                             -- -- 0.7                              CBr.sub.4  -- 0.8                                                                              --  0.4                                                                               1.2                                                                             --  1.2                                                                             -- -- 1.2                                                                              1.2                                                                              --                               Latex Average                                                                            4900                                                                             4300                                                                             2400*                                                                             4700                                                                             4500                                                                             4800                                                                             4500                                                                             4400                                                                             4700                                                                             5500                                                                             5400                                                                             4800                             Particle Size,                                                                Å                                                                         Polydispersity                                                                            1.14                                                                             1.23                                                                            --   1.15                                                                            1.11                                                                             1.11                                                                             1.08                                                                              1.11                                                                            1.07                                                                              1.11                                                                             1.09                                                                             1.09                            __________________________________________________________________________     .sup.a HPMA -- Hydroxylpropyl methacrylate                                    .sup.b HEA -- 2Hydroxyethyl methacrylate                                      .sup.c BIEM -- Isocyanatoethyl methacrylate blocked with 2butanone            ketoxime                                                                      .sup.d DMAEMA -- N,N--dimethyl2-aminoethyl methacrylate                       *Number average measured by turbidity only. All others listed are weight      averages measured by disc centrifuge photosedimentometers (U.S. Pat. No.      4,311,039).                                                              

The resulting latices were cation-exchanged with Amberlite 200C in acidform to remove therefrom virtually all amino intiator fragments andamino monomers. Amberlite 200C is the trademark of Rohm & HaasCorporation for a macroreticular strongly acidic styrene/divinylbenzeneion exchange resin having the following properties: apparent wet densityof 0.8, shipping weight 50 lbs./ft.³, effective size approximately 0.61mm. diam., and moisture content approximately 48%.

Cationic electrocoating baths were operated with each of the ionexchanged latices diluted to 5% N.V. Table III shows the 60° gloss valueversus gel content.

                  TABLE III                                                       ______________________________________                                        Gloss Versus Gel Content of Latex                                             Example No.   Gloss Value (60°)                                                                   % Gel                                              ______________________________________                                        1             82 ± 10   0.6 ± 0.4                                       2             72 ± 11   1.2 ± 1.2                                       3             8 ± 1     20 ± 8                                          4             1            57                                                 5             77 ± 4    0.68 ± .04                                      6             1.8 ± 0.1 24 ± 2                                          7             41 ± 8    0.00 ± 0.00                                     8             6 ± 1     6 ± 2                                           9             5 ± 1     9 ± 1                                           10            86 ± 9    0.03 ± 0.03                                     11            85 ± 4    0.00 ± 0.00                                     12              3 ± 0.3 18 ± 2                                          ______________________________________                                    

The gloss readings were the average of two tests, the error reportedbeing the range divided by two.

It was noted that the panels coated in a 45° bath showed about 5 unitsbetter gloss for Examples 7, 10, and 11, and about 20 units for Example2 than those coated in the lower temperature bath. For the panels ofExamples 1 and 5 no such improvement was observed.

Additionally it was noted that, in general, the lower the gel content,the better the solvent resistance of a cured electrodeposited film(double rubs with methyl ethyl ketone to expose a spot on thesubstrate). However, at very low gel contents, e.g., below 10%, thesolvent-resistance data were scattered considerably.

The instant patent application is related to the followingcommonly-assigned patent applications of even date herewith, thedisclosures of which are incorporated herein expressly by reference:Ser. No. 513,621 and Ser. No. 513,619.

What is claimed is:
 1. A method of electrocoating an electrically conductive surface serving as a cathode in an electrical circuit comprising said cathode, an anode, and an aqueous electrodepositable composition wherein net unidirectional electric current is passed through said circuit for causing deposition of said composition on said cathode and the resulting electrodeposit is baked to cure it, said method being characterized by using as said composition one that comprises synthetic, cation-active, film-forming, amino-stabilized latex particles having latex microgel content that is no substantially above about 2%.
 2. The method of claim 1 wherein said latex is a copolymer containing acrylate and/or methacrylate monomer units and is structurally cation-active by its containing monomer units that have secondary and/or tertiary amino functionality.
 3. The method of claim 1 wherein there is crosslinkability of said resulting electrodeposit provided by hydroxyl groups present that are reactable upon curing of said resulting electrodeposit with blocked/isocyanate groups present therein.
 4. The method of claim 1 wherein said aqueous electrodepositable composition contains a polyether surfactant and particulate material in the form of inorganic particles, plastic particles, and/or powder paint.
 5. The method of claim 1 wherein said aqueous electrodepositable composition is acid-ionized, contains about 1-25% solids, and the latex present therein has average particle size not substantially smaller than about 1000 Å.
 6. The method of claim 1 wherein said aqueous electrodepositable composition is maintained at a temperature of at least about 40° C.
 7. The method of claim 1 wherein said aqueous electrodepositable composition is replenished with a replenishment composition that is like said aqueous electrodepositable composition except that it is richer in solids and lower in acid than said aqueous electrodepositable composition. 